1. Field of the Invention
The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer to a flat mirror finish, and more particularly to a polishing apparatus having a liquid leakage monitoring device.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnections is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 .mu.m wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus, and such a process is called Chemical Mechanical polishing.
Conventionally, a polishing apparatus has a polishing section having a turntable and a top ring which rotate at respective individual speeds. A polishing cloth is attached to the upper surface of the turntable. A semiconductor wafer to be polished is placed on the polishing cloth and clamped between the top ring and the turntable. An abrasive liquid containing abrasive grains is supplied onto the polishing cloth and retained on the polishing cloth. During operation, the top ring exerts a certain pressure on the turntable, and the surface of the semiconductor wafer held against the polishing cloth is therefore polished by a combination of chemical polishing and mechanical polishing to a flat mirror finish while the top ring and the turntable are rotated.
After, for example, one or more semiconductor wafers have been polished, the polishing cloth is processed to recover its original polishing capability. Various processes have been and are being developed for restoring the polishing cloth, and are collectively called "dressing". The polishing cloth is dressed by a dressing tool installed in the polishing apparatus in order to enable the polishing apparatus to perform a good polishing function at all times without undesired degradation of a polishing performance.
Some polishing apparatuses incorporate a cleaning section for conveying semiconductor wafers and cleaning the semiconductor wafers. The cleaning section comprises a workpiece conveying robot for taking a semiconductor wafer out of a cassette and delivering the semiconductor wafer to the polishing section having the turntable and the top ring, a cleaning device for cleaning the semiconductor wafer which has been polished, and a drying device for drying the semiconductor wafer which has been cleaned.
The polishing apparatus further comprises an abrasive liquid supply device which supplies abrasive liquid to the polishing section, and a cooling water supply device which supplies cooling water to the polishing section and the like.
The polishing section, the cleaning section, the abrasive liquid supply device, and the cooling water supply device are in danger of a liquid leakage due to an unexpected failure of some internal devices thereof because they use various liquids or hold various liquids therein. Therefore, it is desirable that when liquid leakage occurs in the above sections and devices i.e. the occurrence, of such leakage being a predetermined malfunction such liquid leakage is quickly detected and stopped.